Depending on how the zip file was prepared, installation of assets varies. OTX files can be double-clicked, after which Outerra handles the installation automatically.

Sometimes people provide assets in unzipped folders, which are typically copied to your packages folder(USERS > Your Name > Outerra > Packages )If you copied them to any other location, Outerra won't see them.

Also, after installing assets you have to exit Outerra and restart the program. Apparently the program only looks for new assets when it starts up.

But depending on the age of the assets, some older assets just don't show up in the asset list because the requirements have evolved and some older assets don't meet the current requirements anymore.

Hopefully one of these possibilities will provide a clue as to why your assets aren't showing up. No doubt there are other possibilities not mentioned here. Please report back when you solve the problem, so others benefit from your research